At least 25% of adults are myopic and for the vast majority the myopia developed after age 6 and prior to age 14. The cost to society is enormous yet we still know very little about why a particular child becomes myopic, what the risk factors are, and exactly how the growth of the eye over those 8 years leads to such a high proportion of myopic eyes. Surprisingly, no longitudinal study of all of the ocular components of refraction over those crucial years has ever been conducted. Today instrumentation is available to make such a study feasible, and recent advances have more clearly identified candidate risk factors. A five year longitudinal study of the refractive error, component optical characteristics and risk factors for myopia in schoolchildren is proposed. The ocular components which contribute to the optical power of the eye, including corneal curvature, anterior chamber depth, vitreal length, axial length, lens thickness, and lens radii of curvature will be measured along with refractive error, tonic accommodation, and specific environmental factors such as near work and family history of myopia. The primary aims of the study are first to identify putative risk factors both prior to and during the development of myopia which might then form a basis for future attempts to treat or retard myopia development, and second, to test the assumption that disproportionate lengthening of the eye is responsible for myopia. This represents the first longitudinal study of all of the components of the eye which are known to contribute to the development of its refractive state. Such a study has the long term objective of answering the questions, "Why does a particular child become myopic?" "What are the risk factors for myopia?" "How can we prevent myopia development in a particular child?"